Place steak in a large dish. Set aside while you make the marinade.
Whisk together the onion, garlic, olive oil, basil, thyme, rosemary, salt, and crushed red pepper. Pour over steak. Refrigerate for at least 30 minutes but not more than 1 hour, 30 minutes.
Preheat grill to 400F to 450F (high) heat. Grill steak 9 minutes on each side or to desired degree of doneness. Remove from the grill and squeeze lemon juice over top. Allow to stand for about 10 minutes before thinly slicing. (Leave the grill on to grill the onions!)
For the sandwiches:
Brush the sliced onions with 1 tablespoon of olive oil; sprinkle with salt and pepper. Grill on the preheated grill for about 7 minutes or until tender. Set aside.
Split the ciabatta rolls; brush with the remaining 2 tablespoons of olive oil. Place cut side down on the hot grill and cook for just a minute or 2, until golden.
Spread hot rolls with mayo (if desired) and then sprinkle with blue cheese. Layer on lettuce, tomato, grilled onions, and the thinly sliced steak. Serve hot!